Conventionally, as a solar radiation shielding film, a heat ray cut film is known. For example, in Patent Document 1, an optical interference film formed by simultaneously extruding a plurality of polymer layers having different refractive indices is described.
In recent years, a transparent laminate film of a multilayer film type is also proposed in which metal oxide layers and metal layers are alternately laminated on one side of a transparent polymer film. For example, in Patent Document 2, a transparent laminate film is disclosed in which seven layers of titanium oxide layers and silver layers are alternately laminated on one side of a PET film, the titanium oxide layers being formed by using a sol-gel method, and the silver layers being formed by using a sputtering method. In the Patent Document 2, it is described that the transparent laminate film is applicable to heat ray cutting.
Further, for example, in Patent Document 3, a technology is disclosed in which, in a heat ray reflecting glass formed by laminating a film having a high heat ray reflectance on a glass substrate, the film has a surface resistivity of 500Ω/□ or less, a dividing groove is formed on the film, and a solar radiation transmittance is 50% or less. In the Patent Document 3, it is described that, although a thermal insulation film allows radio waves to pass through at a groove width of about 50 μm, when the groove width is too small, because an electrical current jumps over a gap of the groove by a displacement current, a thermal insulation film becomes an electrically continuous body.